1. Field of the Invention
The present invention relates to a subscriber transmission apparatus and, more particularly, to an ATM line concentration apparatus in a subscriber transmission system used in a subscriber transmission network for providing broadband services using an ATM technique.
2. Description of the Prior Art
A subscriber transmission system in a subscriber transmission network for providing broadband services including VOD (Video On Demand) using a conventional ATM technique will be described below.
FIG. 1 is a block diagram showing the system configuration of a conventional broadband subscriber transmission network.
The system shown in FIG. 1 includes an ATM switching unit 41, an ATM multiplexer 43 for multiplexing/demultiplexing subscriber information, and subscriber terminals 45 to 48. The ATM multiplexer 43 includes a transmission path termination circuit 56 for terminating a transmission path 49 accommodated in the ATM switching unit 41, transmission path termination circuits 57 to 60 for terminating transmission paths 52 to 55 between the subscriber terminals 45 to 48 and the ATM multiplexer 43, an ATM cell multiplexing/demultiplexing circuit 42 for distributing or multiplexing pieces of ATM information terminated by the transmission path termination circuits 57 to 60, and ATM cell header translation circuits 61 to 64 for replacing the pieces of header information of ATM cells.
In this subscriber transmission apparatus, the total transmission capacity of the transmission path 49 accommodated in the ATM switching unit 41 is equal to the total transmission capacity of the transmission paths 52 to 55 between the subscriber terminals 45 to 48 and the ATM multiplexer 43.
FIG. 2 is a block diagram showing the arrangement of a B-ISDN remote multiplexer disclosed in Japanese Unexamined Patent Publication No. 6-132972, and more specifically, a broadband subscriber transmission network including an ATM switching unit side.
The B-ISDN remote multiplexer shown in FIG. 2 includes an ATM switching unit 141 having part of a subscriber accommodation function set in a remote place, a B-ISDN remote multiplexer 140, and a plurality of subscriber terminals 121 and 122. The ATM switching unit 141 includes a plurality of transmission interface circuits 135, an ATM switch 138, and a signaling processor 139. The B-ISDN remote multiplexer 140 includes a plurality of subscriber circuits 125, a line concentration circuit 127 and a distribution circuit 129 which constitute a concentration/distribution stage, and a transmission interface circuit 132.
The B-ISDN remote multiplexer 140 has a function equivalent to that of the ATM cell multiplexing/demultiplexing circuit 42 in FIG. 1. The B-ISDN remote multiplexer 140 distributes or multiplexes pieces of ATM information transmitted from the ATM switching unit 141 through high-speed transmission paths 133 and 134 and pieces of ATM information transmitted from the subscriber terminals 121 and 122 through line terminating units 123 and subscriber lines 124 on a cell basis.
The signaling processor 139 executes, between the subscriber terminals 121 and 122, a procedure for establishing virtual channels between the B-ISDN remote multiplexer 140 and the ATM switching unit 141 and between the B-ISDN remote multiplexer 140 and the subscriber terminals 121 and 122.
The first problem in the conventional technique is that the utilization efficiency of a transmission path connected to a subscriber terminal cannot be improved for the following reason.
The above network is simply constructed to multiplex/demultiplex pieces of subscriber service information within the range in which the amount of information does not exceed the transmission capacity of the transmission path connected to the ATM switching unit. Therefore, in a subscriber transmission network in which the service utilization efficiency is generally low, transmission capacities must also be assigned to even subscribers for which no services are provided.
The second problem in the conventional technique is that in the invention disclosed in the above official gazette, connection of a specific ATM switching unit, i.e., a unit installed in a remote place, is limited to an ATM switching unit manufactured by the same manufacturer of the specific ATM switching unit.
This is because, part of a signaling procedure between the ATM switching unit and the ATM line concentration apparatus is not based on the disclosed procedure, although an interface is based on the requirements of ATM Forum UNI.